A CdZnTe/MgCdTe double-heterostructure (DH) consisting of a 3 μm thick Cd0.9946 Zn0.0054Te middle layer that is lattice-matched to an InSb substrate has been grown using molecular beam epitaxy. A long carrier lifetime of 3.4 × 102 ns has been demonstrated at room temperature, which is approximately three times as long as that of a CdTe/MgCdTe DH with identical layer thickness. This substantial improvement is due to the reduction in misfit dislocation density in the CdZnTe alloy. In contrast, a CdTe/MgCdTe DH with 3 μm thick CdTe layer grown on an InSb substrate exhibits a strain relaxation of ∼30%, which leads to a wider x-ray diffraction peak, a weaker integrated photoluminescence intensity, and a shorter minority carrier lifetime of 1.0 × 102 ns. These findings indicate that CdZnTe lattice-matched to InSb has great potential as applied to high-efficiency solar cells as well as virtual substrates for high-performance large-area HgCdTe focal plane arrays.
This paper reports the molecular beam epitaxial growth and characterization of high-reflectivity and broad-bandwidth distributed Bragg reflectors (DBRs) made of ZnTe/GaSb quarter-wavelength (lambda/4) layers for optoelectronic applications in the midwave infrared spectral range (2-5 mu m). A series of ZnTe/GaSb DBRs has been successfully grown on GaSb (001) substrates using molecular beam epitaxy (MBE). During the MBE growth, a temperature ramp was applied to the initial growth of GaSb layers on ZnTe to protect the ZnTe underneath from damage due to thermal evaporation. Post-growth characterization using high-resolution x-ray diffraction, atomic force microscopy, and transmission electron microscopy reveals smooth surface morphology, low defect density, and coherent interfaces. Reflectance spectroscopy results show that a DBR sample of seven lambda/4 pairs has a peak reflectance as high as 99.0% centered at 2.56 mu m with a bandwidth of 517 nm.
The ability of a single monolithic semiconductor structure to emit or lase in a broad spectrum range is of great importance for many applications such as solid-state lighting and multi-spectrum detection. But spectral range of a laser or light-emitting diode made of a given semiconductor is typically limited by its emission or gain bandwidth. Due to lattice mismatch, it is typically difficult to grow thin film or bulk materials with very different bandgaps in a monolithic fashion. But nanomaterials such as nanowires, nanobelts, nanosheets provide a unique opportunity. Here we report our experimental results demonstrating simultaneous lasing in two visible colors at 526 and 623 nm from a single CdSSe heterostructure nanosheet at room temperature. The 97 nm wavelength separation of the two colors is significantly larger than the gain bandwidth of a typical single II-VI semiconductor material. Such lasing and light emission in a wide spectrum range from a single monolithic structure will have important applications mentioned above.